1. Field of the Invention
This invention relates to new and improved catalysts for the production of vinyl acetate by reaction of ethylene, oxygen and acetic acid.
2. Background Information Including Description of Related Art
It is known to produce vinyl acetate by reaction of ethylene, oxygen and acetic acid using a catalyst consisting of metallic palladium and gold supported on a carrier. While the process utilizing such a catalyst is capable of producing vinyl acetate at fair levels of productivity, such productivity levels are limited by the production of undesirable by-products, particularly carbon dioxide. The production of any product or by-product can be expressed as percent selectivity, defined as the amount of such product expressed as a percentage of the theoretical maximum which could be produced from the reactants. Thus, any expedient which results in a reduced production of carbon dioxide expressed as lower percent CO.sub.2 selectivity, is very desirable.
The following references may be considered material to the invention claimed herein.
U.S. Pat. Nos. 3,775,342 issued Nov. 27, 1973, and 3,822,308 issued Jul. 2, 1974, both to Kronig et al., each discloses a method of making vinyl acetate catalysts comprising treating a support simultaneously or successively with a solution A containing dissolved salts of noble metals such as palladium and gold, and a solution B containing compounds able to react on the support with the noble metal salts to form water insoluble compounds of the metals, treating such water-insoluble compounds with a reducing agent to convert the water-insoluble noble metal compounds to the metals, washing the catalyst to remove water-soluble compounds, and applying an alkali metal compound e.g. an alkali metal carboxylate before or after treatment with the reducing agent. Solution A can optionally also contain salts of any of several other metals, including copper.
U.S. Pat. No. 5,332,710, issued Jul. 26, 1994, to Nicolau et al., discloses a method of preparing a catalyst useful for the production of vinyl acetate by reaction of ethylene, oxygen and acetic acid, comprising impregnating a porous support with water soluble salts of palladium and gold, fixing the palladium and gold as insoluble compounds on the support by immersing and tumbling the impregnated support in a reactive solution to precipitate such compounds, and subsequently reducing the compounds to their metallic form.
U.S. Pat. No. 5,347,046, issued Sep. 13, 1994, to White et al., discloses catalysts for the production of vinyl acetate by reaction of ethylene, oxygen, and acetic acid, comprising a palladium group metal and/or a compound thereof, gold and/or a compound thereof, and copper, nickel, cobalt, iron, manganese, lead or silver, or a compound thereof, preferably deposited on a support material.